// A simple module to replace `Backbone.sync` with *localStorage*-based
// persistence. Models are given GUIDS, and saved into a JSON object. Simple
// as that.

// Generate four random hex digits.
function S4() {
	return (((1 + Math.random()) * 0x10000) | 0).toString(16).substring(1);
};

// Generate a pseudo-GUID by concatenating random hexadecimal.
function guid() {
	return (S4() + S4() + "-" + S4() + "-" + S4() + "-" + S4() + "-" + S4() + S4() + S4());
};

// Our Store is represented by a single JS object in *localStorage*. Create it
// with a meaningful name, like the name you'd give a table.
var Store = function(name) {
	this.name = name;
	var store = localStorage.getItem(this.name);
	this.data = (store && JSON.parse(store)) || {};
};

_.extend(Store.prototype, {

	// Save the current state of the **Store** to *localStorage*.
	save : function() {
		localStorage.setItem(this.name, JSON.stringify(this.data));
	},

	// Add a model, giving it a (hopefully)-unique GUID, if it doesn't
	// already
	// have an id of it's own.
	create : function(model) {
		if (!model.id)
			model.set(model.idAttribute, guid());
		this.data[model.id] = model;
		this.save();
		return model;
	},

	// Update a model by replacing its copy in `this.data`.
	update : function(model) {
		this.data[model.id] = model;
		this.save();
		return model;
	},

	// Retrieve a model from `this.data` by id.
	find : function(model) {
		return this.data[model.id];
	},

	// Return the array of all models currently in storage.
	findAll : function() {
		return _.values(this.data);
	},

	// Delete a model from `this.data`, returning it.
	destroy : function(model) {
		delete this.data[model.id];
		this.save();
		return model;
	}

});

// Override `Backbone.sync` to use delegate to the model or collection's
// *localStorage* property, which should be an instance of `Store`.
Backbone.sync = function(method, model, options) {

	var resp;
	var store = model.localStorage || model.collection.localStorage;

	switch (method) {
		case "read" :
			resp = model.id ? store.find(model) : store.findAll();
			break;
		case "create" :
			resp = store.create(model);
			break;
		case "update" :
			resp = store.update(model);
			break;
		case "delete" :
			resp = store.destroy(model);
			break;
	}

	if (resp) {
		options.success(resp);
	} else {
		options.error("Record not found");
	}
};